amd64/160802: USB installation image fails to boot if BIOS is not GPT compatible - 9.0-BETA2

[Camillo Särs]

>Number:         160802
>Category:       amd64
>Synopsis:       USB installation image fails to boot if BIOS is not GPT compatible - 9.0-BETA2
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    freebsd-amd64
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Sep 18 13:20:05 UTC 2011
>Closed-Date:
>Last-Modified:
>Originator:     Camillo Särs
>Release:        9.0-BETA2
>Organization:
>Environment:
N/A - does not install
>Description:
The 9.0-BETA2 USB installation image uses a GPT partition table, which is not bootable on systems that have a buggy BIOS.  E.g. Gigabyte GA-D510UD.

Attempting to boot the system while the USB stick is connected will cause the BIOS to fail - the failure mode depends upon the bug in the BIOS.

The Gigabyte GA-D510UD will lock up completely when it runs into a GPT partition table of this kind.  The pmbr does not match the CHS setup that the BIOS expects.

Related bug: bin/115406: [patch] gpt(8) GPT MBR hangs award BIOS on boot


>How-To-Repeat:
- Download 9.0-BETA2 USB installation image, install on USB stick
- Connect USB stick to system with GPT issues, attempt to boot the system
- Boot fails

Compare this to the 8.2-RELEASE image, which uses MBR and thus boots correctly.
>Fix:
This problem can only be fixed by trying to circumvent the buggy BIOSes.  The most reliable way would be to revert the USB image to MBR format.  Another alternative is to ensure that the pmbr of the GPT partition table contains a correct CHS configuration, but the GPT pmbr may still cause problems on some BIOSes.

>Release-Note:
>Audit-Trail:
>Unformatted: